Is non-alcoholic fatty liver disease a reflection of what we eat or simply how much we eat?

Non-alcoholic fatty liver disease (NAFLD) is an increasingly common and potentially serious condition, which has emerged with the obesity epidemic. This disease can progress to cirrhosis and hepatocellular cancer. Associated comorbidities, such as cardiovascular disease and type 2 diabetes, are common. Obesity is the key risk factor and diet appears to be a critical factor in the pathogenesis of NAFLD. We reviewed studies undertaken on human subjects investigating which dietary components initiate excess hepatic triglyceride deposition. Most experimental diets used high-calorie excesses, or extreme proportions of fat or carbohydrate, not typical of current dietary patterns. Hypercaloric diets, where the additional calories were predominantly either fat or carbohydrates, increased intrahepatocellular lipids. The type of fat appeared important, with diets high in saturated fatty acids favoring hepatic fat accumulation which was substantially lower with polyunsaturated fatty acids. The effect of dietary fructose on markers of NAFLD did not appear to be worse than that of glucose. The initiation of excess hepatic triglycerides is likely to be a complex interaction of energy and nutrients with more than one dietary factor involved. It was not possible to disentangle the hepatic effects of excess energy from that of different macronutrient distributions in current literature. Further investigation is needed to determine the type of diet that is likely to lead to the development of NAFLD. A better understanding of the contribution of diet to pathogenesis of NAFLD would better inform prevention strategies.